Patent GB-775015-A (GB)
Title: Process for oxidising mercaptans or mercaptides to disulphides in a two-phase system consisting of a light hydrocarbon oil phase and an aqueous alkali metal hydroxide phase
IPC: C07B45/06
Filed: 1954-03-12
Abstract: Oil-soluble mercaptans or alkali-metal mercaptides derived from oil-soluble mercaptans are oxidized to disulphides by means of oxygen in the absence of an oxidation catalyst, the mercaptans or mercaptides being initially in a two-phase system, one phase of which is formed by a light hydrocarbon oil having a boiling-point or end-boiling point not exceeding 350 DEG  C., and the other phase by a stable, homogeneous aqueous alkaline solution containing an alkali-metal phenolate as hereinafter defined, at least 2 mols. of free alkali-metal hydroxide per litre of the solution and not more than 54 per cent by volume of water based on the total volumes of the components of the solution before they are mixed with each other, the oil and aqueous phases being maintained in intimate contact during the oxidation.  In one embodiment the light hydrocarbon oil contains mercaptans initially and is thereby sweetened and in another, the alkaline solution is one previously used in removal of mercaptans from oils and is thereby regenerated.  The alkali metal phenolates are those derived from phenol or a monohydric alkylated phenol containing a total of not more than 3 carbon atoms in the alkyl group(s) and having no other substituents.  The aqueous solutions preferably contain 2-5 mols. of free hydroxide per litre and are normally used in a ratio of 0.05 to 5 vols. per volume of oil.  The oxidation may be effected batch-wise or continuously under ordinary or higher pressure and preferably at 10-45 DEG  C.  The oxygen required may be dissolved in the hydrocarbon oil before or during its contacting with the aqueous solution.  The two phases may be intimately mixed by spraying one into the other or by means of a suitably packed tower or a centrifugal mixer.  The process may be applied to the sweetening of mercaptan-containing gasolines, kerosine and gas oil.  An anti-oxidant is preferably added when a cracked or reformed gasoline is used.  The oils are normally pretreated with dilute alkali to remove aromatic mercaptans and H2S.  Those oils containing more than 0.05 per cent mercaptan sulphur are preferably pre-treated to remove the excess mercaptans suitably by means of an aqueous solution containing the alkali hydroxide and phenolate present in the aqueous solution used in the oxidation. Following the oxidation, the aqueous alkaline solution is separated from the light oil, which contains the oxidized mercaptans, and is suitable for re-use.  In order to maintain the phenolate content constant, the aqueous alkaline solution may be subsequently used in oxidations, or extractions without oxidation, of oils whose phenolic content is relatively high or low as required.  A number of oxidations are described wherein a debutanised cracked gasoline is contacted with aqueous solutions of sodium or potassium hydroxide and the corresponding cresolate or xylenolate in air at 20 DEG  C.  The results are compared graphically with those obtained using aqueous solutions of similar composition which do not, however, have the specified proportions of alkali and water.  A phase diagram is given of the KOH : water : cresol ternary system.  Specification 712,056, [Group III], is referred to.ALSO:Oil-soluble mercaptans or alkali-metal mercaptides derived from oil-soluble mercaptans are oxidized to disulphides by means of oxygen in the absence of an oxidation catalyst, the mercaptans or mercaptides being initially in a two-phase system, one phase of which s formed by a light hydrocarbon oil having a boiling point or end-boiling point not exceeding 350 DEG C. and the other phase by a stable, homogenous aqueous alkaline solution containing an alkali-metal phenolate as hereinafter defined, at least 2 moles of free alkali-metal hydroxide per litre of the solution and not more than 54 per cent by volume of water based on the total volumes of the components of the solution before they are mixed with each other, the oil and aqueous phases being maintained in intimate contact during the oxidation.  In one embodiment the light hydrocarbon oil contains mercaptans initially and is thereby sweetened and in another, the alkaline solution is one previously used in removal of mercaptans from oils and is thereby regenerated.  The alkali metal phenolates are those derived from phenol or a monohydric alkylated phenol containing a total of not more than 3 carbon atoms in the alkyl group (S) and having no other substituents.  The aqueous solutions preferably contain 2-5 moles of free hydroxide per litre and are normally used in a ratio of 0.05 to 5 vols. per volume of oil.  The oxidation may be effected batch-wise or continuously under ordinary or higher pressure and preferably at 10 DEG -45 DEG C.  The oxygen required may be dissolved in the hydrocarbon oil before or during its contacting with the aqueous solution.  The two phases may be intimately mixed by spraying one into the other or by means of a suitably packed tower or a centrifugal mixer.  The process may be applied to the sweetening of mercaptancontaining gasolines, kerosine and gas oil.  An anti-oxidant is preferably added when a cracked or reformed gasoline is used.  The oils are normally pretreated with dilute alkali to remove aromatic mercaptans and H2S.  Those oils containing more than 0.5 per cent mercaptan sulphur are preferably pre-treated to remove the excess mercaptans suitably by means of an aqueous solution containing the alkali hydroxide and phenolate present in the aqueous solution used in the oxidation.  Following the oxidation, the aqueous alkaline solution is separated from the light oil, which contains the oxidized mercaptans, and is suitable for reuse.  In order to maintain the phenolate content constant, the aqueous alkaline solution may be subsequently used in oxidations, or extractions without oxidation, of oils whose phenolic content is relatively high or low as required.  A number of oxidations are described wherein a debutanized cracked gasoline is contacted with aqueous solutions of sodium or potassium hydroxide and the corresponding cresolate or xylenolate in air at 20 DEG C.  The results are compared graphically with those obtained using aqueous solutions of similar composition which do not, however, have the specified proportions of alkali and water.  A phase diagram is given of the KCH:water:cresol ternary system.  Specification 712,056 is referred to.